U.S. patent application number 13/789773 was filed with the patent office on 2013-07-25 for mirror and related euv systems and methods.
This patent application is currently assigned to CARL ZEISS SMT GMBH. The applicant listed for this patent is Carl Zeiss SMT GmbH. Invention is credited to Heiko Feldmann, Johannes Ruoff.
Application Number | 20130188163 13/789773 |
Document ID | / |
Family ID | 44677897 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130188163 |
Kind Code |
A1 |
Ruoff; Johannes ; et
al. |
July 25, 2013 |
Mirror and Related EUV Systems and Methods
Abstract
A mirror for EUV radiation includes a mirror body, which has at
least one EUV radiation-reflecting region and at least two EUV
radiation-permeable regions. A spatial separation of the
illumination and imaging beam paths is possible with small angles
of incidence and a large object-side numerical aperture.
Inventors: |
Ruoff; Johannes; (Aalen,
DE) ; Feldmann; Heiko; (Aalen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carl Zeiss SMT GmbH; |
Oberkochen |
|
DE |
|
|
Assignee: |
CARL ZEISS SMT GMBH
Oberkochen
DE
|
Family ID: |
44677897 |
Appl. No.: |
13/789773 |
Filed: |
March 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2011/066667 |
Sep 26, 2011 |
|
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13789773 |
|
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61387544 |
Sep 29, 2010 |
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Current U.S.
Class: |
355/67 ; 359/350;
359/353 |
Current CPC
Class: |
G03F 7/70225 20130101;
G02B 5/0891 20130101; G03F 7/70283 20130101; G03F 7/70066
20130101 |
Class at
Publication: |
355/67 ; 359/350;
359/353 |
International
Class: |
G02B 5/08 20060101
G02B005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2010 |
DE |
102010041623.1 |
Claims
1. A mirror, comprising: a mirror body comprising at least one EUV
radiation-reflecting region and at least two EUV
radiation-permeable regions, wherein: the radiation-permeable
regions are arranged disconnectedly in the mirror body; the
radiation-permeable regions have an envelope delimiting an area
which overlaps with at least 30% of the totality of the at least
one radiation-reflecting region; and the mirror is an EUV
mirror.
2. The mirror of claim 1, wherein the mirror has a conjugated EUV
radiation-reflecting region for each EUV radiation-permeable
region, and each EUV radiation-permeable region is transferrable by
a rotation about an axis of symmetry into its corresponding
conjugated EUV radiation-reflecting region.
3. The mirror of claim 2, wherein each EUV radiation-permeable
region is arranged symmetrically with respect to the axis of
symmetry to its respective conjugated EUV radiation-reflecting
region.
4. The mirror of claim 3, wherein the mirror comprises a large
number of radiation-permeable regions and radiation-reflecting
regions conjugated thereto.
5. The mirror of claim 2, wherein the mirror comprises a large
number of radiation-permeable regions and radiation-reflecting
regions conjugated thereto.
6. The mirror of claim 5, wherein the mirror comprises a large
number of radiation-permeable regions and radiation-reflecting
regions conjugated thereto.
7. The mirror of claim 1, wherein at least a part of the
radiation-permeable regions is arranged on a circle about the axis
of symmetry.
8. The mirror of claim 1, wherein the radiation-permeable regions
are arranged so that their common center of gravity coincides with
an axis of symmetry.
9. The mirror of claim 2, wherein the radiation-permeable regions
are arranged so that their common center of gravity coincides with
the axis of symmetry.
10. An optical system, comprising: a mirror according to claim 1,
wherein the optical system is an illumination optical system
configured to illuminate an object field with EUV radiation via the
mirror.
11. A system, comprising: an illumination optical system comprising
a mirror according to claim 1, wherein the system is an EUV
projection exposure system.
12. An optical system, comprising: a mirror according to claim 1,
wherein the optical system is a projection optical system
configured to image an object field into an image field via the
mirror.
13. The optical system of claim 12, wherein the mirror is close to
a pupil.
14. A system, comprising: a projection optical system comprising a
mirror according to claim 1, wherein the system is an EUV
projection exposure system.
15. An optical system, comprising: a first optical system
configured to illuminate an object field with EUV radiation, the
first optical system comprising at least one pupil facet mirror,
the EUV radiation in the first optical system having at least one
specific beam course to produce a specific illumination setting;
and a second optical system configured to image the object field
into an image field, wherein at least one of the optical systems
comprises a mirror comprising at least one EUV radiation-permeable
region in the beam path of the other optical system so that at
least a part of the EUV radiation in this optical system is guided
through the at least one EUV radiation-permeable region.
16. The optical system of claim 15, wherein the first optical
system is an illumination optical system and the second optical
system is a projection optical system.
17. The optical system of claim 16, wherein the mirror is in the
projection optical system.
18. The optical system of claim 16, wherein the mirror is in the
illumination optical system.
19. A system, comprising: an optical system according to claim 15,
wherein the system is an EUV projection exposure system.
20. A method, comprising: using an EUV projection exposure system
to project at least a portion of a reticle onto a light-sensitive
material, wherein the EUV projection exposure system comprises a
mirror according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of, and claims priority
under 35 USC 120 to, International Patent Application Serial Number
PCT/EP2011/066667, filed Sep. 26, 2011, which claims benefit under
35 USC 119 of German Patent Application 10 2010 041 623.1, filed
Sep. 29, 2010. International Patent Application Serial Number
PCT/EP2011/066667 also claims priority under 35 USC 119 to U.S.
Ser. No. 61/387,544, filed Sep. 29, 2010. The entire contents of
International Patent Application Serial Number PCT/EP2011/066667
are incorporated by reference herein.
FIELD
[0002] The disclosure relates to a mirror for EUV radiation. The
disclosure also relates to an illumination optical system, a
projection optical system, an optical system, and an EUV projection
exposure system. The disclosure further relates to a method for
producing a microstructured or nanostructured component and a
component produced by such a method.
BACKGROUND
[0003] Mirrors for EUV radiation and an EUV projection exposure
system are known from EP 1 927 892 A1. An X-ray microscope is known
from U.S. Pat. No. 6,522,717 B1.
SUMMARY
[0004] The disclosure provides a mirror for EUV radiation which
results in improved optical quality when used in an EUV projection
exposure system.
[0005] In one aspect, the disclosure provides a mirror for EUV
radiation, which includes a mirror body including at least one EUV
radiation-reflecting region and at least two EUV
radiation-permeable regions. The radiation-permeable regions have
an envelope delimiting an area which overlaps with at least 30% of
the totality of the at least one radiation-reflecting region.
[0006] It was recognized according to the disclosure that, when
used a lithography mask, the ability of a reticle to reflect drops
sharply from a specific angle of incidence of the EUV radiation
used for illum. An oblique illumination moreover leads to a
considerable telecentric error.
[0007] However, with a perpendicular illumination of the reticle
(in other words, with a course of the main beam of the illumination
optical system parallel to the optical axis and with the course of
the main beam perpendicular to the reticle) due to constructive
constraints obscurations of the beam path in the illumination
and/or projection optical system occur.
[0008] The main beam of an object field point (in other words, a
specific point of the reticle) is defined here as the connection
line between this object field point and a center of a pupil of the
illumination optical system.
[0009] The disclosure provides a mirror for EUV radiation which
includes at least one EUV radiation-reflecting region and at least
two (such as at least three, at least four, at least five) EUV
radiation-permeable regions. The EUV radiation-permeable regions
are, for example, configured here as through-openings in the mirror
body. The radiation-permeable regions are, for example, arranged
disconnected in the mirror body. The radiation-permeable regions
are, for example, arranged distributed over the mirror body in such
a way that their envelope delimits an area, which overlaps with at
least 30% (such as at least 40%, at least 50%, at least 60%, at
least 70%, at least 80%, at least 90%) of the area of the totality
of the radiation-reflecting regions.
[0010] It is possible to have a configuration of the mirror, which
is inverted with respect to this, in which the reflecting and
permeable regions are just interchanged. With this inverted
configuration, a large number (such as at least two, at least
three, at least four, at least five) of EUV radiation-reflecting
regions are provided. The radiation-reflecting regions may, for
example, be disconnected. They may, for example, be mechanically
linked to one another by cross-struts. They can, for example, be
applied to a braiding-type holder. In this configuration of the
mirror, the EUV radiation-permeable areas make up, for example, at
least 50% (such as at least 60%, at least 70%, at least 80%, at
least 90%) of the total area of the mirror.
[0011] Using the mirror disclosed herein, it is possible, even with
a high numerical aperture of the illumination optical system, to
illuminate the reticle at a small angle of incidence without an
obscuration of the EUV radiation reflected by the reticle. Using
the mirror according to the disclosure, it is, for example,
possible to guide the zero diffraction order of the EUV radiation
reflected by the reticle, free of obscuration, through the
projection optical system.
[0012] A spatial separation of the illumination and imaging beam
path is possible using the mirror according to the disclosure.
[0013] In some embodiments, a mirror has a conjugated EUV
radiation-reflecting region for each of the EUV radiation-permeable
regions. Each EUV radiation-permeable region can be transferred by
a rotation about an axis of symmetry into the EUV
radiation-reflecting region which is conjugated thereto. The mirror
has an associated EUV radiation-reflecting region for each of the
EUV radiation-permeable regions. The EUV radiation-reflecting
region is also called the region complementary to its respective
radiation-permeable region. In particular, the region on the
mirror, which is associated with a specific radiation-permeable
region and in which the zero diffraction order of the radiation
reflected by the reticle is imaged, is called the conjugated
region. The terms "complementary region" and "conjugated region"
are merely used to describe the subject matter disclosed herein.
The corresponding regions do not necessarily have defined
mechanical limitations. The complementary regions, in particular
the conjugated regions, are in each case arranged at predetermined
positions relative to the radiation-permeable regions on the
mirror. In principle, the radiation reflected on the reticle, in
particular the higher diffraction orders, can fall on any regions
of the mirror. With knowledge of the structures of conventionally
used reticles, it can, however, be predetermined by a targeted
arrangement of the radiation-permeable and radiation-reflecting
regions, which diffraction orders of the reflected light contribute
to the projection of these reticles into the image field. It is, in
particular, possible to configure the mirror for a bright field
illumination or for a dark field illumination.
[0014] In some embodiments, each EUV radiation-permeable region is
arranged symmetrically with respect to the axis of symmetry to the
respective EUV radiation-reflecting region conjugated thereto. This
arrangement is advantageous for bright field applications, as it
ensures that at least the zero diffraction order of the radiation
reflected on the reticle can in each case fall precisely on an EUV
radiation-reflecting region. Thus, at least a part of the
point-mirrored illumination pupil, in particular the entire
point-mirrored illumination pupil is a component of the imaging
beam path. The mirror, in particular the arrangement of the EUV
radiation-reflecting and the EUV radiation-permeable regions, may
be adapted to specific, predetermined reticles, in particular to
typically used reticles. With a given reticle with a typical
reticle structure, in particular with a known structure to be
imaged, by a suitable arrangement of the EUV radiation-permeable
regions on the mirror, it can also be achieved, in particular,
that, in addition to or alternatively to the zero diffraction
order, other diffraction orders, in particular the +/-first
diffraction order of the radiation reflected on the reticle in each
case falls precisely onto an EUV radiation-reflecting region.
[0015] If an "axis of symmetry" and a "symmetrical arrangement" of
the regions is referred to here and below, this is, in each case,
also taken to mean a correspondingly distorted configuration of the
mirror, which is used with an oblique position of the mirror
relative to the main beam of the beam path.
[0016] It is possible, with the mirror according to the disclosure,
to illuminate the reticle in such a way that the angle of the main
beam (CRA, chief ray angle) is smaller than the arcsin of the
object-side numerical aperture (NAO), CRA<arcsin (NAO).
[0017] In some embodiments, the mirror has a large number of
radiation-permeable regions and radiation-reflecting regions
conjugated thereto. This allows a large number of different
illumination settings, and it also allows for a reduction in the
relative fraction of each individual radiation-permeable region and
the respective radiation-reflecting region conjugated thereto of
the radiation used in total to image the object field in the image
field. The influence on the imaging quality, which it has, if a
diffraction order of the reflected radiation associated with an
individual, specific radiation-permeable region impinges by chance
again on a radiation-permeable region and is therefore not
reflected, is thereby reduced. As a result, the imaging quality can
be made more robust overall. For this purpose, it is advantageous,
in particular, if the radiation-permeable regions are in each case
as small as possible in comparison to the total optically usable
(in other words, reflecting) mirror face.
[0018] In some embodiments, a mirror has at least a part of the
radiation-permeable regions arranged on a circle about the axis of
symmetry. This can provide a particularly uniform, homogenous
illumination of the reticle can be achieved. The
radiation-permeable regions may, in particular, be arranged
equidistantly on the circle here. An equidistant arrangement of an
odd number of radiation-permeable regions leads here precisely to a
bright field configuration as, in this case, a radiation-reflecting
region opposes, with respect to the axis of symmetry, each
radiation-permeable region.
[0019] Accordingly, an equidistant arrangement of an even number of
radiation-permeable regions leads to a dark field configuration, as
a further radiation-permeable region precisely opposes, with
respect to the axis of symmetry, each radiation-permeable region.
The zero diffraction order of the radiation reflected by the
reticle from each radiation-permeable region therefore impinges, at
least partially (such as completely) precisely on a
radiation-permeable region again, is therefore not reflected by the
mirror and therefore does not contribute to the imaging of the
object field in the image field.
[0020] Moreover, the radiation-permeable regions may be arranged on
a plurality of concentric circles about the axis of symmetry. As a
result, different illumination settings with different angles of
incidence are made possible. Interference effects can thereby be
reduced.
[0021] In some embodiments, the radiation-permeable regions are
arranged so that their common center of gravity coincides with the
axis of symmetry. As a result, it becomes possible to illuminate
the reticle in such a way that the main beam of the illumination
radiation has an angle of incidence of 0.degree..
[0022] In one aspect, the disclosure provides an illumination
optical system for illuminating an object field with EUV radiation
using a mirror as disclosed herein.
[0023] In another aspect, the disclosure provides a projection
optical system for imaging an object field into an image field
using a mirror as disclosed herein. The mirror can be arranged
close to a pupil An arrangement of a mirror M close to a pupil is
present when the following condition is fulfilled:
P(M)=D(SA)/(D(SA)+D(CR)).gtoreq.0.5.
[0024] D(SA) is the sub-aperture diameter of a beam pencil emitted
from an object field point at the site of the mirror M and D(CR) is
the maximum spacing of main beams of an effective object field,
imaged by the imaging optical system, measured in a reference plane
of the optical system, on the surface of the mirror M. The
reference plane may be a plane of symmetry or a meridional plane of
the imaging optical system. The definition of the parameter P(M)
corresponds to that given in WO 2009/024 164 A1.
[0025] In a field plane, P(M) equals zero. In a pupil plane, P(M)
equals one.
[0026] It is possible to ensure by an arrangement close to the
pupil that at least the zero diffraction order of the radiation
reflected by the reticle in each case falls completely on a
radiation-reflecting region.
[0027] In one aspect, the disclosure provides an optical system for
an EUV projection exposure system, wherein the optical system
includes a mirror as disclosed herein.
[0028] In another aspect, the disclosure provides an EUV projection
exposure system which includes an optical system including a mirror
as disclosed herein.
[0029] Advantages of such an optical system and such an EUV
projection exposure system correspond to those noted above.
[0030] In one aspect, the disclosure provides a method for
producing a component using a projection exposure system disclosed
herein.
[0031] In a further aspect, the disclosure provides a component
produced by a method which includes using a projection exposure
system as disclosed herein.
[0032] Advantages of such a method and component correspond to
those noted above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Embodiments of the disclosure will be described in more
detail below with the aid of the drawings, in which:
[0034] FIG. 1 shows a schematic view of the components of an EUV
projection exposure system for EUV lithography;
[0035] FIG. 2 shows a schematic view of a section enlargement of a
beam path of illumination light and imaging light of the projection
exposure system according to FIG. 1 in the region of a reflecting
object to be imaged in the projection exposure in the form of a
reticle;
[0036] FIG. 3 shows a schematic view of a section enlargement of a
beam path of illumination light and imaging light similar to FIG.
2, but with an alternative guidance of the beam path;
[0037] FIGS. 4A and 4B show schematic views of a mirror according
to the disclosure according to a first embodiment;
[0038] FIGS. 5A and 5B show schematic views of a mirror according
to the disclosure in accordance with a further embodiment;
[0039] FIGS. 6 and 7 show schematic views of further embodiments of
a mirror;
[0040] FIG. 8 shows a schematic view of the use of a mirror
according to the disclosure in combination with a Schwarzschild
optical system; and
[0041] FIG. 9 shows a schematic view of a further embodiment of a
mirror.
DETAILED DESCRIPTION
[0042] FIG. 1 schematically shows, in a meridional section, the
components of a projection exposure system 1 for microlithography.
An illumination system 2 of the projection exposure system 1, apart
from a beam source 3, includes an illumination optical system 4 for
exposing an object field 5 in an object plane 6. A reticle 7, which
is arranged in the object field 5 and is held by a reticle holder
8, only shown section-wise, is exposed here.
[0043] A projection optical system 9 is used to image the object
field 5 in an image field 10 in an image plane 11. A structure on
the reticle 7 is imaged on a light-sensitive layer of a wafer 12,
which is arranged in the region of the image field 10 in the image
plane 11 and is held by a wafer holder 13 also shown
schematically.
[0044] The radiation source 3 is an EUV radiation source, which
emits EUV radiation 14. The wavelength of the emitted useful
radiation of the EUV radiation source 3 is in the range of 5 nm to
30 nm. Other wavelengths, which are used in lithography, and are
available for the suitable light sources, are also possible. The
radiation source 3 may be a plasma source, for example a DPP source
or an LPP source. A radiation source, which is based on a
synchrotron, can also be used as the radiation source 3.
Information on a radiation source of this type is found by the
person skilled in the art, for example in U.S. Pat. No. 6,859,515
B2. A collector 15 is provided to bundle the EUV radiation 14 from
the EUV radiation source 3.
[0045] The EUV radiation 14 is also called illumination light or
imaging light.
[0046] The illumination optical system 4 includes a field facet
mirror 16 with a large number of field facets 17. The field facet
mirror 16 is arranged in a plane of the illumination optical system
4, which is optically conjugated to the object plane 6. The EUV
radiation 14 is reflected by the field facet mirror 16 to a pupil
facet mirror 18 of the illumination optical system 4. The pupil
facet mirror 18 has a large number of pupil facets 19. With the aid
of the pupil facet mirror 18, the field facets 17 of the field
facet mirror 16 are imaged in the object field 5.
[0047] For each field facet 17 on the field facet mirror 16, there
is precisely one associated pupil facet 19 on the pupil facet
mirror 18. A light channel is configured between a field facet 17
and a pupil facet 19, in each case. The facets 17, 19 of at least
one of the facet mirrors 16, 18 may be switchable. They may, in
particular be tiltably arranged on the field facet mirror 16, 18.
It is possible here to make only one part tiltable, for example at
most 30%, at most 50% or at most 70% of the facets 17, 19. It may
also be provided to make all the facets 17, 19 tiltable. The
switchable facets 17, 19 are, in particular, the field facets 17.
By tilting the field facets 17, the allocation thereof to the
respective pupil facets 19 and therefore the configuration of the
light channels may be varied. For further details of the facet
mirrors 16, 18 with tiltable facets 17, 19, reference is made to DE
10 2008 009 600 A1.
[0048] For further details of the illumination optical system 4,
reference is also made to DE 10 2008 009 600 A1.
[0049] The beam path of the EUV radiation 14 in the illumination
optical system 4 and the projection optical system 9 and, in
particular, the structural arrangement of the field facet mirror 16
and the pupil facet mirror 18 cannot be inferred from FIG. 1.
[0050] The reticle holder 8 can be displaced in a controlled manner
in such a way that, during the projection exposure, the reticle 7
can be displaced in a displacement direction in the object plane 6.
Accordingly, the wafer holder 13 can be displaced in a controlled
manner in such a way that the wafer 12 can be displaced in a
displacement direction in the image plane 11. As a result, the
reticle 7 and the wafer 12 can be scanned, on the one hand, through
the object field 5 and, on the other hand, the image field 10. The
displacement direction will also be called the scanning direction
below. The displacement of the reticle 7 and the wafer 12 in the
scanning direction can preferably take place synchronously with one
another.
[0051] The projection optical system 9 includes a large number of
projection mirrors, which are not shown in FIG. 1. The projection
optical system 9 includes, in particular, at least three, in
particular at least five, projection mirrors. It can, in
particular, have at least six, seven or eight projection
mirrors.
[0052] The projection optical system 9 includes, in particular, a
mirror 20, which will be described in more detail below.
[0053] The mirror 20 has a mirror body 21 with a mirror face 24
with a large number of EUV radiation-permeable regions 22 and
respective associated EUV radiation-reflecting regions 23. The
respective EUV radiation-reflecting region 23 associated with an
EUV radiation-permeable region 22 is also called a region
complementary to the EUV radiation-permeable region 22. In
particular, the radiation-reflecting region 23 associated with a
specific radiation-permeable region 22 on the mirror 20, in which
the 0 diffraction order of the radiation 14 reflected by the
reticle 7 is imaged, is called the conjugated region 23. Obviously,
the EUV radiation-reflecting region 23, which is complementary to
an EUV radiation-permeable region 22, does not only include the
respectively conjugated region 23, which is designated for viewing
in the figures. In principle, the complementary region in each case
includes the total mirror face 24.
[0054] The number of radiation-permeable regions 22 in the mirror
20 in particular corresponds precisely to the number of pupil
facets 19 on the pupil facet mirror 18. However, this is not
absolutely necessary. In particular in the case of switchable
facets 17, 19, the number of radiation-permeable regions 22 may
also be more or less than the number of pupil facets 19 on the
pupil facet mirror 18 and/or the field facets 17 on the field facet
mirror 16. In general, the mirror 20 has at least two EUV
radiation-permeable regions 22. These are configured as
through-openings in the mirror body 21. The EUV
radiation-reflecting regions 23 may be configured as part regions
of the reflecting mirror face 24 configured continuously apart from
the through-openings 22. The EUV radiation-reflecting regions 23
may, in particular, be connected. The EUV radiation-permeable
regions 22 are, in particular, arranged in a disconnected manner in
the mirror body 21. The mirror face 24 may be convex, planar or
concave.
[0055] The radiation-permeable regions 22 are arranged spaced apart
from an axis 25 of symmetry of the mirror 20, in particular in such
a way that each EUV radiation-permeable region 22 can be
transferred into the respective EUV radiation-reflecting region 23
conjugated thereto by a rotation about the axis 25 of symmetry. The
axis 25 of symmetry is, in particular, perpendicular to the mirror
face 24. In a central region, in other words in the region of the
point where the axis 25 of symmetry is pierced, the mirror 20, in
other words the mirror face 24, is, in particular, reflecting. In
principle, it is also conceivable for the mirror 20 to be provided
with a central through-opening.
[0056] The mirror 20 has a discrete, at least two-fold rotational
symmetry with respect to the axis 25 of symmetry. It may, in
particular, have an odd, for example a three-fold, five-fold or
seven-fold rotational symmetry. Higher-fold symmetries are also
possible. In the case of an odd rotational symmetry, each EUV
radiation-permeable region 22 is arranged symmetrically with
respect to the axis 25 of symmetry to the respective EUV
radiation-reflecting region 23 conjugated thereto.
[0057] The through-openings 22 have a shape which precisely
corresponds to the shape of the pupil facets 19 on the pupil facet
mirror 18. They are, in particular, circular. An oval, in
particular an elliptical configuration, is also possible.
[0058] The arrangements of the radiation-permeable regions 22 on
the mirror 20 and those of the pupil facets 19 on the pupil facet
mirror 18 are advantageously adapted to one another.
[0059] Taken together, the radiation-permeable regions 22 cover at
most 50%, in particular at most 40%, in particular at most 30%, in
particular at most 20%, in particular at most 10%, of the mirror
face 24.
[0060] In the embodiments shown in FIGS. 4A, B and 5A, B, the EUV
radiation-permeable regions 22 are arranged on a circle about the
axis 25 of symmetry. In general, at least one part of the
radiation-permeable regions 22 is arranged on a circle about the
axis 25 of symmetry. They are, in particular, arranged
equidistantly on the circle. They may also be arranged on a
plurality of concentric circles about the axis of symmetry. The
radiation-permeable regions 22 are, in particular, arranged in such
a way that their common centre of gravity coincides with the axis
25 of symmetry. The totality of the radiation-permeable regions 22
can be described by an outer envelope 35. The radiation-permeable
regions 22 are, in particular, arranged in such a way on the mirror
20 that their outer envelope 35 delimits an area, which overlaps
with at least 30%, in particular at least 40%, in particular at
least 50%, in particular at least 60%, in particular at least 70%,
in particular at least 80%, in particular at least 90%, of the area
of the totality, in other words the combination of the
radiation-reflecting regions 23, in particular the total mirror
face 24.
[0061] A mirror 20 with three circular radiation-permeable regions
22 is shown for illustration in FIG. 4A, B. Accordingly, a mirror
20 with five respective circular radiation-permeable regions 22 is
shown in FIG. 5A, B. Furthermore, the radiation-permeable regions
22 and the radiation-reflecting regions 23 conjugated thereto in
each case are furthermore shown in FIGS. 4A and 5A for
illustration, encircled, and numbered consecutively, the respective
radiation-reflecting region 23 conjugated to a specific
radiation-permeable region 22 being designated with the same number
and an r placed thereafter. The encircling of the conjugated
regions 23 serves merely for illustration and has no structural
correspondence on the actual mirror 20. In particular, the total
mirror face 24, depending on the structure of the reticle 7 and,
connected therewith, the position of the diffraction orders of the
radiation 14 reflected thereby, can form an EUV
radiation-reflecting region 23. The radiation-reflecting regions 23
associated with the radiation-permeable regions 22 may, in
particular, be configured to be overlapping and/or connected. The
mirrors 20 shown in FIGS. 4A and 5A have a three-line or five-line
rotational symmetry. The radiation-permeable regions 22 are
therefore in each case arranged symmetrically with respect to the
axis 25 of symmetry to the radiation-reflecting regions 23
conjugated thereto.
[0062] In the embodiment according to FIG. 6, the mirror 20 has
three sector of a circle-shaped radiation-permeable regions 22.
[0063] In the embodiment according to FIG. 7, the mirror 20 has
four sector of a circle-shaped radiation-permeable regions.
[0064] The function of the mirror 20 according to the disclosure is
shown schematically in FIG. 3. The EUV radiation 14 from a light
channel configured between one of the field facets 17 and the pupil
facets 19, in each case, passes through the associated EUV
radiation-permeable region 22 through the mirror 20, is reflected
on the reticle 7 and impinges in the region of the pupil plane 26,
which is, in particular, an exit pupil plane of the illumination
optical system 4 and an entry pupil plane of the projection optical
system 9, on the radiation-reflecting region 23, which is
conjugated to the radiation-permeable region 22, from which it is
further reflected via the projection optical system 9.
[0065] FIG. 2 shows a beam path by way of example, such as can be
achieved, for example, with the mirror 20 according to FIGS. 4A and
4B. EUV radiation 14.sub.1, 14.sub.2 and 14.sub.3 is shown by way
of example, which, in each case, passes through one of the
through-openings 22 through the mirror 20. It is shown in this
regard that the beam courses shown in FIG. 2 are only a projection
into the plane of the drawing and therefore do not depict the
incline to the plane of the drawing. Thus, in particular the beam
14.sub.1 passing through the mirror 20 does not coincide with the
beam 14.sub.3 reflected back onto the mirror 20, but is skew with
respect to the latter. Correspondingly, the beam 14.sub.3 passing
through the mirror 20 is skew with respect to the beam 14.sub.1
reflected back onto the mirror 20. Furthermore, the beam 14.sub.2
passing through the mirror 20 is skew with respect to the beam
14.sub.2 reflected back onto the mirror 20.
[0066] The mirror 20 is, in particular, arranged close to the pupil
in the projection optical system 9. There applies, in particular
P(M).gtoreq.0.5, in particular P(M).gtoreq.0.7, in particular
P(M).gtoreq.0.9.
[0067] The mirror 20 is, in particular, arranged in a pupil plane
26. This ensures that the radiation 14 coming from a pupil facet 19
of the pupil facet mirror 18 in the region of the mirror 20 is at
least approximately focused, and therefore at least the zero
diffraction order of the associated radiation reflected on the
reticle 7 impinges in a predetermined, limited region on the mirror
20. In the case of a bright field configuration, for example
according to one of the FIG. 4, 5 or 6, the mirror 20 is configured
in such a way that at least the zero diffraction order of the
radiation 14 reflected on the reticle 7 from a radiation-permeable
region 22 impinges precisely on the radiation-reflecting region 23
conjugated thereto and is therefore imaged by the projection
optical system 9 in the image field 10. It can be achieved owing to
the arrangement of the mirror 20 close to the pupil that the
illumination and imaging beam paths are at least partially, in
particular completely, spatially separated from one another. The
separation is, in particular, the same for all the field points. In
particular, the beam paths of the zero diffraction order run in
regions completely spatially separated from one another.
[0068] As an alternative to an arrangement of the mirror 20 in the
pupil plane 26, it is also possible to arrange the mirror 20 spaced
apart from a pupil plane 26. This generally leads to a field
dependency of the illumination, in other words, the illumination is
no longer homogeneous in the entire object field. These effects of
an incompletely imaged pupil can, in this case, be completely
corrected, in particular by a field-dependent and
structure-dependent correction method, which is known as "optical
proximity correction" (OPC), as long as an adequate fraction of a
minimum number of diffraction orders is transmitted for each field
point. In a correction method of this type, by a single
case-dependent structure adaptation of the mask, the image thereof
on the wafer is improved. In particular, imaging errors are
compensated and therefore corrected.
[0069] In a dark field configuration, the zero diffraction order of
the radiation 14 reflected on the reticle 7, as shown, for example,
in FIG. 7, impinges on the mirror 20 precisely on a further
radiation-permeable region 22 and is therefore not reflected by the
mirror 20.
[0070] An optical system 27 according to the disclosure includes
the illumination optical system 4 and a projection optical system
28. The projection optical system 28 includes at least one mirror
with at least one EUV radiation-permeable region 22, which is
arranged in the beam path of the illumination optical system 4 in
such a way that at least a part of the EUV radiation 14 is guided
in the illumination optical system through this EUV
radiation-permeable region 22. The beam path in the illumination
optical system 4 is therefore guided, in other words, in such a way
that the EUV radiation 14 passes through the at least one
radiation-permeable region 22, before it is reflected by the
reticle 7, and the reticle 7 is imaged by the projection optical
system 9 in the image field 10. It is, in particular, provided that
the projection optical system 28 is configured according to the
projection optical system 9 described above.
[0071] When using the projection exposure system 1, the reticle 7
and the wafer 12, which carries a light-sensitive coating for the
illumination light 14, are provided. At least one portion of the
reticle 7 is then projected with the aid of the projection exposure
system 1 onto the wafer 12. The reticle is thus illuminated with
EUV radiation 14 in such a way that the main beam (CRA, chief ray
angle) of the EUV radiation 14 impinges on the reticle 7 at an
angle of incidence of at most 6.degree., in particular at most
3.degree., in particular at most 1.degree., in particular
0.degree.. The angle of incidence is defined here as the angle
between the main beam of the beam bundle being used to illuminate
the reticle 7 and a normal 29 on the reticle 7. The angle of
incidence of the main beam is, in particular, smaller than the
object-side numerical aperture, CRA<arcsin (NAO).
[0072] During the projection of the reticle 7 onto the wafer 12,
the reticle holder 8 and/or the wafer holder 13 can be displaced in
the direction parallel to the object plane 6 or parallel to the
image plane. The displacement of the reticle 7 and the wafer 12 may
preferably take place synchronously with respect to one
another.
[0073] Finally, the light-sensitive coating exposed by the
illumination light is developed on the wafer 12. A microstructured
or nanostructured component, in particular a semiconductor chip, is
produced in this manner.
[0074] As an alternative to use in a projection exposure system,
the mirror 20 according to the disclosure can also be used in an
inspection device, in particular for inspecting reflective
lithography masks or to inspect exposed wafer substrates. The image
field 10 of the projection optical system 9 is, in this case, an
inspection object field of the inspection device.
[0075] As shown schematically in FIG. 8, the mirror 20 according to
the disclosure can also be used in combination with a Schwarzschild
optical system 30, in particular a Schwarzschild lens system. The
Schwarzschild lens system includes a primary mirror 31 and a
secondary mirror 32. The primary mirror 31 is, in particular,
convex. The secondary mirror 32 is, in particular concave. The
secondary mirror 32 has a through-opening 33 for the EUV radiation
14.
[0076] The mirror 20 according to the disclosure may be provided as
a folding mirror in a system of this type. It can, in particular,
be arranged as part of the illumination optical system 4 in the
beam path of the projection optical system 9 or as part of the
projection optical system 9 in the beam path of the illumination
optical system 4. It may be exchangeable. As a result, it is
possible, in particular, to change between bright and dark field
configurations. A system of this type can, in particular, be used
in an inspection device for inspecting reflective lithography masks
or for inspecting exposed wafer substrates.
[0077] FIG. 9 shows an inverted configuration of the mirror 20a.
The mirror 20a includes a large number of radiation-reflecting
regions 23. The radiation-reflecting regions 23 are topologically
disconnected.
[0078] The radiation-reflecting regions 23 are held relative to one
another by a holding mechanism 34. The holding mechanism is, in
particular configured in a strut-like manner. They may be linear or
arcuate, in particular, arc of a circle-shaped. They may also be
configured in a braiding-like manner. The holding mechanism 34 is
as thin as possible to cause as little shading as possible. They
cover, in particular, an area, which makes up at most 30%, in
particular at most 25%, in particular at most 20%, in particular at
most 15%, in particular at most 10%, in particular at most 5%, of
the total face of the mirror 20a. The holding mechanism may, in
particular, be made of aluminium, invar steel, titanium, copper,
ceramics or carbon fibres. The holding mechanism 34 is, in
particular, dimensioned in such a way that the radiation-reflecting
regions 23 are reliably fixed with respect to one another.
[0079] In principle, it is conceivable to configure the mirror 20a
monolithically, i.e. to make the radiation-reflecting regions 23
topologically connected.
[0080] In this embodiment, various, i.e. radiation-permeable
regions 22 associated with different radiation-reflecting regions
23 may be topologically connected. They may, in particular, apart
from the holding mechanism 34, form a connected, in particular a
path-wise connected, but not simply connected overall region. In
other words, the overall region of the radiation-permeable regions
22, apart from the holding mechanism 34, is connected, in
particular path-wise connected. However, individual
radiation-permeable regions 22 are, to a limited extent, and in
particular, at least partially, separated from one another by the
holding mechanism 34. Thus, the mirror 20a also has a large number,
in particular at least two, in particular at least three, in
particular at least four, radiation-permeable regions 22.
[0081] The mirror 20a is, in particular, part of the illumination
optical system 4. It may be arranged in the beam path of the
projection optical system 9. The mirror 20a is, in particular,
arranged in the beam path of the projection optical system 9 in
such a way that at least a part of the EUV radiation 14 in the
projection optical system 9 is guided through the at least one EUV
radiation-permeable region 22. The radiation-reflecting regions 23
may act here in the projection optical system 9 as obscuration
stops.
[0082] In this embodiment, the radiation-reflecting regions 23 are
arranged in such a way that the radiation 14 reflected by them on
the reticle 7 after reflection on the reticle 7, in other words in
the beam path of the projection optical system 9, falls precisely
on the radiation-permeable region 22. This is in turn taken to mean
that predetermined diffraction orders of the radiation 14 reflected
on the reticle 7, in particular the zero diffraction order, fall on
the radiation-permeable region 22. Obviously, the
radiation-reflecting regions 23 may also be arranged on the mirror
20a in such a way that, additionally or alternatively to the zero
diffraction order, the +/-first diffraction order of the radiation
14 reflected on the reticle 7 falls on the radiation-permeable
region 22.
* * * * *